The present invention relates generally to chemiresistor and more specifically to phthalocyanine film chemiresistors. A chemiresistor is a device which exhibits the electrical characteristics of a resistor whose conductance is modulated by the presence or absence of some chemical species in contact with the device. Such devices have been sought for many years as very simple and sensitive chemical sensors for process control and environmental monitoring applications. It is well known that semiconductors exhibit characteristic electronic conductivities which are strongly affected by ambient chemical vapors. Indeed, much effort has been expended worldwide investigating heated metal oxide semiconductors such as tin oxide and zinc oxide as vapor sensors. In spite of extensive development of these devices, they have proven to be less than ideal since they do not detect vapors very selectively or at concentrations below a few parts per million, and they are not readily suited for integration into conventional monolithic silicon technology.
Organic semiconductor films containing phthalocyanine are an alternative to heated metal oxides. Devices employing sublimed or evaporated films have high sensitivity to vapors. However, these devices typically exhibit slow response to vapor concentration changes.
An improved semiconductor film may be produced for use in a chemiresistor using substituted phthalocyanines and the Langmuir-Blodgett film deposition technique. An example of this, using phthalocyanines with carbon substitutions on the phthalocyanine ring is seen in Baker et al., IEEE Proceedings, Vol. 130, Pt. 1, No. 5, October 1983.
However, the use-of carbon-carbon bonds to attach substituents to the phthalocyanine ring is disadvantageous because the creation of such bonds involves expensive and difficult processing steps. Ether, or thioether, linked substituents allow for substantially more economical and reliable manufacturing processes.